380 GEOGRAPHICAL SYSTEMS 
tent of the eastern coast of Africa, the farthest ex- 
plored portion of which took an easterly direction. 
This direction was hypothetically extended, till it 
was made to join the eastern extremity of Asia. 
Thus the Indian, or Erythrean sea, was enclosed as 
in a vast basin ; and in Africa, as in Asia, an ex- 
panse of Terra Incognita became on every side the 
limit of the known world. This school, however, 
shook off entirely the previous belief of an unin- 
habitable zone. Ptolemy gives numerous positions 
under and beyond the equator, and even approach- 
ing to the southern tropic. Admitting that many, 
or all of them, are extended too far to the south, 
this does not the less indicate his own conviction, 
that the region immediately under the line could 
be passed through and inhabited. 
Ptolemy appears to have been the first who 
formed a correct idea of the whole course of the 
Nile. He throws up entirely its western deriva- 
tion, and assigns to its fountains their proper place 
in the vast range of the Mountains of the Moon. 
He represents also, like Eratosthenes, the rivers 
Astapus and Astaboras, (the modern Bahr-el- Azrek 
and Tacazze), as falling into it from the east, and 
only errs in making them, by their junction, form 
Meroe into an island. Westward from the Nile, 
he describes the vast range of Libya Interior, 
watered by the great rivers Gir and Niger. It 
has been generally understood, that this tract com- 
